Method of recovering hydrocarbons by in situ combustion

ABSTRACT

The invention provides a method for recovering hydrocarbons from a geological formation having combustible organic material. A passageway is established from a point in the formation, through same, and to the surface of the ground. The combustible organic material is ignited. Oxygen-containing gas is passed into the resulting combustion zone by establishing at lower than normal formation pressure, a pressure drop from the combustion zone to a point outside the formation through the passageway. The temperature of combustion is controlled to only partially volatilize the organic material. The gases resulting from the partial combustion are passed to the surface of the ground. The method is preferred to recover hydrocarbons and other chemicals from a coal stratum and/or from an oil sand. In the preferred specific embodiment, the method is applied to recovering hydrocarbons from a coal stratum and a separate oil sand stratum, separated by a stratum of kerogen. In the latter heat of combustion is by conduction passed from the coal stratum to the oil sand stratum.

United States Patent [72] Inventors Messman, 31 Ellsworth Road, Larchmont,

862,617 Sept. 8, 1969 Aug. 17, 1971 [21 App]. No. [22] Filed I 45] Patented [54] METHOD OF RECOVERING HYDROCARBONS BY 2,841,375 7/1958 Salomonsson 166/256 X 3,010,707 11/1961 Craighead et al. 166/258 X 3,145,772 8/1964 Huitt 166/259 X 3,283,814 11/1966 Schlicht et al. 166/259 X Primary Examiner-Stephen J. Novosad AttorneyJohn H. Widdowson ABSTRACT: The invention provides a method for recovering hydrocarbons from a geological formation having combustible organic material. A passageway is established from a point in the formation, through same, and to the surface of the ground. The combustible organic material is ignited. Oxygen-containing gas is passed into the resulting combustion zone by establishing at lower than normal formation pressure, a pressure drop from the combustion zone to a point outside the formation through the passageway. The temperature of combustion is controlled to only partially volatilize the organic material. The gases resulting from the partial combustion are passed to the surface of the ground. The method is preferred to recover hydrocarbons and other chemicals from a coal stratum and/or from an oil sand. in the preferred specific embodiment, the method isapplied to recovering hydrocarbons from a coal stratum and a separate oil sand stratum, separated by a stratum of kerogen. In the latter heat of combustion is by conduction passed from the coal stratum to the oil sand [56] References Cited UNITED STATES PATENTS 2,584,605 2/1952 Merriam etal. l66/258X 2,695,163 11/1954 Pearce etal.... 166/259X- 2,734,579 2/1956 Elkins 166/251 2,780,449 2/1957 Fisher et al. 166/259 2,788,956 4/1957 Pevere et a1. 166/259 stratum.

F Oz CONTAIN/Nb- GAS 72 Llpwps FUEL P CovERy in a "ii-ki 'P.;-'e2 42 70 KFQOL'rE'IV PATENTEDAUGIHBY: 7 3.599714 sum 1 OF 2 CONTA l/Vl/V GA 5 29 awa Rzcovcnv O; x/Fu LIUIDS RECOVER? Krnoaew J GOA L- INVENTORS ROGER L. MESSMAN 6o KARL E. BECKER '6 BY HENRY c. MESSMAN ATTORNEY METHOD OF RECOVERING HYDROCARBONS BY IN SITU'COMBUS TION In the prior art, methods are known to recover hydrocarbons and other volatile chemicals from coal by in situ destructive distillation of the coal, the heat for such being supplied by partial combustion of the coal. Also, it is known to mine hydrocarbons from a stratum of oil sand in a similar manner, that is, partial combustion of the petroleum in situ with heat, and resulting combustion gases being used to enrich a gaseous fluid for recovery of hydrocarbons therefrom in a surface operation, and with heat resulting from combustion being used to. aid in the recovery of a liquid portion of the petroleum. Also, it is known in the art to completely burn coal in situ in a stratum of same to produce heat, and pass the resulting heat by conduction into an oil sand overlying or underlying same to lower petroleumviscosity and aid in the recovery thereof from the oil sand by normal means of elevating the liquid fluids to the surface, and treating resulting gaseous fluid at the surface to recover the desired hydrocarbon constituents therefrom. The known processes of the prior art have not been successful. Until the invention hereof no procedure existed to optimumly partially burn the coal (normally bituminous) in a coal stratum to result in destructive distillation of the coal, recovering the off gases produced .and utilizing the heat of combustion by conduction and convection 'to mine and recover hydrocarbons from petroleum in an oil sand overlying and/or underlying the coal stratum and separated therefrom by a kerogen strata, under controlled conditions of coal combustion, that is, temperature of combustion regulated by the available oxygen in an oxygen controlled and containing gas (principally air), regulated by the amount of oxygen in the gas and/or by the volume of the oxygen-containing gas, or the water vapor content thereof, such being passed into the coal stratum from the surface of the ground. The prior art has attempted complete combustion of the coal, anticipating condensation of the coal volatiles in the oil sand strata as a hindrance to petroleum recovery. We have found the opposite to be true, and such is an important consideration in the process of our invention.

This invention utilizes thermo, chemical, and thermochemical processing of combustible organic material in situ and is normally directed at processing bituminous coal in a stratum above or below petroleum in an oil sand stratum, with the two being separated by a kerogen stratum. Other combustible materials found in geological formations to which the invention appliesare for example, sulfur, anthracite coal,peat, lignite and the like. It is an important feature of the invention that the oxygen-containing gas passed into the combustion zone in the combustible material stratum is done so by creating a vacuum (pressure below atmospheric) at the surface of the ground in the outlet end portion of a passageway established into the combustion zone, through the stratum of combustible organic material (bituminous coal), through the oil sand, and to the surface of the ground. This results we have found, in being able to control combustion, especially the temperature thereof, to provide for optimum mining of the coal and recovery of the petroleum in the oil sand. By in effect pulling the oxygen-containing gas down into the combustion zone. the volume thereof is completely controllable, and thus the amount of oxygen available for the partial combustion of the coal in situ. And we have found this makes the process completely controllable, because inert gases can be introduced to lower the percentage of oxygen in the air passed into the combustion zone, or oxygen-rich gas can be introduccd into the air to increase combustion and temperature, or the water vapor content of the oxygen-containing gas can be easily controlled by introducing steam to control combustion and the temperature thereof. The gases resulting from combustion of the coal are passed through the coal stratum where they are enriched, as a result of heat of convention and evaporation of coal volatiles thereinto, and thence through the oil sand where they are further enriched in gaseous hydrocarbon constituents, and then to the surface where by condensationand/or absorption,-desired recoverable hydrocarbons and other chemicals are removed, with the remainder being available as a fuel gas. Volatiles from combustion gases condensed in the coal stratum and/or oil sand stratum become enriched, collected and pumped to the surface and conveniently from the same passageways or wells used for introducing oxygencontaining as and withdrawing production gases, or the condensates lower the viscosity of the petroleum so that it is more easily recovered by collecting and pumping methods, and a greater percentage of such is ultimately recovered from the oil sand. We have found that important benefits of the invention are that it practically and economically increases reserves of recoverable naturally occurring materials in geological formations, and offers a method to recover such from formations that up to now were considered too small, too thin, too deep, too steeply pitched, or others which are considered not amendable to economic exploitation by the conventional methods of recovery.

Spaced wells are established by conventional methods and means into the geological formation from which the combustible organic material is recovered by the new method of the invention. A passageway through the formation or stratum between the wells is established by conventional methods and means. For example, the passagewaysor channels through the seam ofstratum of coal can be made by drilling, shooting and/or preferably by fracturing, utilizing the usual high-pressure oil methods. This is desirably done from the input well (oxygen-containing gas input), to the chimney well (the outlet from the coal stratum). At the surface, at the outlet of the established passageway, gaseous fluid-pumping means is used to establish a pressure drop from the oxygen-containing gas-inlet, through the coal seam or oil sand to the surface, and in operation as a result of this pressure drop oxygen-containing gas is passed to a point of combustion where the organic material in the seam has been ignited to supply the oxygen for combustion. Complete controllability of the process results. It is easy to control volume, oxygen, richness, and water vapor of the gas to result in combustion controlled as to temperature and as to the recoverable volatiles produced therefrom as a result ofthe destructive distillation of the organic material, coal and/or petroleum.

It is an object of this invention to provide a new method for recoveringhydrocarbons from geological formations.

Another object of this invention is to provide a new method for recovering stratified combustible organic material in geological formations.

It is another object of this invention to provide a new method of mining bituminous coal and petroleum from geological formations.

A further object of this invention is to provide a new method of thermally, and thermochemically recovering and mining coal, from a seam or stratum of same, and petroleum from an oil sand stratum containing such, by controlled partial volatilization of the coal by partially burning same, with resulting heat of conduction and heat of convection in the resulting heated gases being utilized in recovering the petroleum hydrocarbons from the oil sand.

Another object of this invention is to provide a new vacuum operating procedure to recover hydrocarbons and other chemicals from geological formations having combustible organic material therein, especially bituminous coal and petroleum in an oil sand, wherein a pressure lower than atmospheric is established in the outlet of the chimney well into the formation, and as a result passing oxygen-containing gas into the input well and into the combustion zone in the coal stratum, such resulting in a pressure drop through the organic material stratum at pressure lower than normal formation pressure.

Yet another object of the invention is to provide a new completely controllable thermal and thermochemical method of mining coal and/or petroleum which is economical and simple to operate and which results in optimum recovery.

Other objects and advantages of the new invention will become apparent to those skilled in the art upon reading this disclosure, and it is to be understood that this disclosure is not to unduly limit the invention.

Drawings accompany and are a part of the disclosure. They depict schematically preferred specific embodiments of the new method of the invention. They are not to unduly limit the invention. In the drawings,

FIG. 1 is a schematic flowsheet depicting the new method of the invention as applied to mining coal.

FIG. 2 is a schematic flowsheet depicting the new method of the invention applied to mining coal and petroleum where the oil sand having the petroleum is above the coal seam or stratum with a kerogen stratum separating same.

FIG. 3 is a schematic flowsheet depicting the new method of the invention applied to mining coal and petroleum in an oil sand where the coal is above the oil sand, with a stratum of kerogen separating same.

FIG. 4 is a schematic flowsheet depicting the method of the invention applied to mining coal and petroleum in an oil sand, utilizing a centrally located input well surrounded by two or more chimney wells.

In the following, a description of preferred specific embodiments of the invention is made with reference to the drawings whereon the same reference numerals and identifying indicia are used to indicate the same stratum, structure, and the like. It is to be understood that such specific description is not to unduly limit the invention.

The method of recovering hydrocarbons from geological formations having a combustible organic material of the invention, can be applied to suitable stratum of any geological age, and particularly and preferably to those of Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, and tertiary systems and to either or both'of the stratified bituminous coal and oil sand having petroleum therein found in these geological formations. Oil fields of numerous geological ages commonly have coal seams of varying grades of bituminous coal, ligneous deposits, or veins of similar organic combustible matter, such often being found associated closely with the sand stratum having petroleum therein. In the process of the invention the bituminous coal seams, ligneous deposits or other combustible organic matter not only are mined by destructive distillation in situ, but provide and act as the source of heat energy for the thermal drive utilized in the new method of the invention to mine the petroleum in the stratified oil sand, by lowering the viscosity of same in its liquid fluid phase and by partial distillation of same to produce and recover a gaseous fluid phase along with the gaseous fluid products resulting from the in situ destructive distillation of the combustible organic material in the coal seam, ligneous deposits, or other similar combustible organic material containing stratum.

The new method of the invention is very advantageously carried out in oil fields such as commonly exist in northeastern Oklahoma, southeastern Kansas, and western Missouri, where at relatively shallow depths there exist stratified bituminous coal seams and oil sands, normally separated by shale, rock or kerogen formations. For example, in northeastern Oklahoma at relatively shallow depths of only a few hundred feet, the Burbank, Chelsea, and Bartlesville oil sands are stratified above and below with bituminous coal seams excellently located for carrying on the method of the invention to mine the bituminous coal by destructive distillation in situ and to provide the heat energy to mine the petroleum and the oil sand both by heat of conduction and convection, and the method of the invention is especially advantageous in this application because these oil sands are notoriously tight and compact, resulting in slow and low recovery. In southeastern Kansas atvery shallow depths a similar situation is present with the normally tight and compact Weizer, Peru, Squirrel or Prue, Ardmore, Burbank, Chelsea, and Bartlesville oil sands at less than 300 feet, and deeper as in Oklahoma, Kansas, and western Missouri, the Burgess oil sand, which is also relatively tight and compact. In western Missouri at less than 400 feet in depth, it is common to find the Squirrel, Chelsea, Bartlesville, and Burgess oil sands with seams of bituminous coal above and below each oil sand stratum, and such formations have been found to be most ideal in which to practice the new method of the invention. These Pennsylvanian systems are preferred in carrying on the new method of the invention. However, the other geological systems can be advantageously mined for hydrocarbons by the method of the invention, and economically and efficiently. It is common with these geological formations to have stratum or layers of shale or rock, and the like, between the coal seam and oil sand, and it is through such shale or rock that heat is passed in carrying on the new method of the invention by conduction from the coal seam to the oil sand stratum, such heat resulting from the destructive distillation of the bituminous coal by limited or partial combustion of same in situ. Heat by convection is passed from the coal seam via the gaseous fluid products of the destructive distillation of the bituminous coal to the oil sand, wherein the petroleum is partially distilled to enrich the gaseous fluids. In carrying on the method of the invention, optimum conditions in most instances have been found to be a limited and controlled combustion of the coal to produce a maximum of recoverable hydrocarbons from both the coal and petroleum in the oil sands. It has been found that combustion temperature in excess of l,650 F. is unfavorable from the standpoint of recovery economically.

The new method of the invention of recovering hydrocarbons from a geological formation having therein a combustible organic material is essentially one of establishing a passageway from a point in the formation, through the formation, and to ground surface. Then, the combustible material in the formation is ignited. An oxygen-containing gas is passed into the combustion zone in the formation resulting from igniting the combustible material therein, and an important and essential step to optimum mining is that the oxygen-containing gas is passed into the combustion zone by establishing at lower than the normal pressure in the geological formation, a pressure drop from the combustion zone to a point outside the formation through the passageway, and usually to the ground. The temperature of combustion is controlled to only partially volatilize the organic material in the formation. This can conveniently be accomplished by regulating the amount of oxygen in the oxygen-containing gas and/or the amount of the oxygencontaining gas passed into the combustion zone in the formation. The gaseous fluids produced by the combustion (the destructive distillation) are passed to the surface of the ground for recovery of hydrocarbon material therein.

In practicing the new method of the invention in what has been found a highly preferred embodiment, stratified geologi cal formations are mined, one of them being an oil sand having petroleum and the other a bituminous coal seam relatively close thereto underground. It is usual that these strata are separated by a stratum of shale or rock. Two wells are established into both strata through the shale or rock, and in another highly preferred similar embodiment, a central well is so established surrounded by a plurality of other wells into both strata to be mined. Passageways for gaseous fluids are provided from one of the wells to the other. Stratum which is not porous enough to pass gaseous fluids in sufficient quantity can be made sufficient in any suitable manner, for example, by fracturing this formation in any suitable manner known to the art. The flow passageway is in sequence down one of the wells, through the stratum which in operation is burned (coal), up or down the other well to the stratum (oil sand) which will be mined while utilizing heat of conduction and convection, and up and out of the latter formation to the surface of the ground for recovery of the volatile hydrocarbons. The organic material in the formation to be burned (coal seam) is ignited in any suitable manner near the input well for oxygen-containing gas (air). The oxygen-containing gas is passed into combustion zone in the coal seam resulting from the ignition, as a result of lowering pressure with exhaust means at or near the surface of the ground, so as to provide a pressure drop from the combustion zone in the coal seam to the surface of the ground through the passageway. A pressure at or near ground outlet is established at less than atmospheric to in turn result in a pressure in the coal seam at lower than formation pressure. In operation, the temperature of combustion of the coal is controlled to in turn control the amount of its destructive distillation by regulating the amount of oxygen in the oxygen-containing gas passed to the combustion zone in the coal seam and/or by controlling the volume of oxygen-containing gas passed into the combustion zone. In this type of application of the new method of this invention, combustion temperature is normally higher than in mining coal only, but desirably not over l,650 F., the close control resulting from drawing the combustion supporting gases into the coal seam has been found to be the key to optimum recovery from the mining.

The combustion gases produced in the coal seam are passed through the passageway in same, heating and volatilizing other organic material, with the resultant gaseous fluids passing out of the coal seam up or down the well spaced from the air input or furnace well and into the oil sand, and through same to partially volatilize the petroleum and enrich the gaseous fluids, and to heat the oil sand to lower the viscosity of the petroleum liquid fluids therein to enhance recovery of same by collecting and pumping means in the usual manner. The final resulting gaseous fluids are passed up and out of the ground to collecting, condensing and recovery means at or near the ground level. Heat resulting from burning coal in situ is passed to the oil sand by conduction through the rock or shale stratum therebetween to partially volatilize the petroleum and/or to result in lowering the viscosity of the liquid fluids for recovery of same by usual means.

In operation the flame or burning is started at the furnace well in the coal seam, and is carried through the bed toward the other well and the passageways or channel established therethrough becomes enlarged by the burning of the combustible matter. This permits increasing the volume of the combustion-supporting gas passed into and through the passageways, and enhances recovery.

While the oxygen-containing gas employed in the new method of the invention to support combustion in the coal seam or stratum can be any suitable composition, normally air or oxygen-enriched air is satisfactory and desirable. It has been found that yields of desirable products from the destructive distillation of the coal in situ are normally increased with most bituminous coals in Pennsylvanian and Mississippian geological formations when warm air of relatively high humidity is employed, and in most applications air 90 percent saturated with water at 1 to 135 F. is preferred. Atmospheric air can be heated in any suitable manner, and to increase water content to a desired amount, water or saturated steam can be added thereto. Saturated steam and oxygen can be mixed with the air to result in satisfactory moisture content and temperature for optimum combustion of the coal in situ.

In practicing the invention, the well supplying oxygen-containing gas is the input or furnace well, and a well utilized to pass resulting vaporized hydrocarbons to the oil sand stratum or to the surface is called the output or chimney well. It has been found desirable and important to success in the use of the new method of the invention to establish a substantial and reliable path or paths for the gases supporting combustion and the gaseous fluids produced by combustion through the coal seam and the oil sand stratum, if the oil sand and/or coal strata are not permeable therefor, or an adjacent formation is not satisfactorily permeable to provide the passageway. Permeability can be accomplished by known methods. Horizontal drilling through the underground stratum can be accomplished to provide the flow paths through the geological stratum, if desired. The known formation-fracturing methods have been found very advantageous and desirable to establish desired passageways from the furnace to the chimney wells, and vice versa, in the coal and oil sand strata, and for added economy and efficiency fracturing in both directions, that is,

into the formation from both directions is desirable. Hydraulic lifting of the overburden or within'the seam has been found to produce excellent passageways for practicing the invention. A noncompressible fluid, for example, oil or water, in practicing these methods is forced down the wells in communication with the coal seam and the oil sand stratum. Pumps are employed to force the fracture fluids into the stratum under a pressure greatly in excess of that existing in the seam or sand. In this fracturing, the pressure and force exerted works as a hydraulic jack and causes over burden to lift or causes the seam or stratum to separate along its lines of weakness, resulting in the formation of a channel or channels between the furnace or input, and output or chimney wells, or adjacent formation channels to serve the purpose.

Another means of establishing communication between the wells through the coal seam and oil sand stratum, etc., is by the use of explosive bullets which are fired from a well into the stratum to penetrate the seam and provide the passageway channels. Directional shooting can also be employed to establish the channels and passageways.

Any combination of these methods to make formations permeable can be employed, and from a practical standpoint this is important, because the fracturability of the oil sand and coal seam determines the maximum effective distance of well spacing in carrying out the new method of the invention.

The new method of the invention in any of its embodiments, that is, as applied to mining coal and/or petroleum from underground geological formations, can be implemented it has been found by employing cyclic circulation through the passageways present or established through the oil sand and/or coal seam, such having been found to minimize plugging of such passageways and to otherwise improve operation. Such cyclic circulation can take the form of simply interrupting normal circulation in operation with an occasional rest period, allowing draining, etc. by gravity to open or better condition the channels or passageways through the formation, or such can take the form of reversing direction of gaseous and/or liquid fluid flow through the passageways or channels in the formations. It has been found to be undesirable normally to introduce air into the formation served by a production well during the reversed circulation, and during such, an inert gas, nitrogen or fuel gas previously produced and accumulated, can be employed.

Referring now to the drawings, which diagrammatically and schematically illustrate typical preferred geological formations to which the method of the invention can be applied, and in particular to FIG. 1, a furnace well 6 is established from ground level 8 downwardly through overlying formations to communicate with a coal seam 10. It is well to note that the same or similar apparatus, structures, geological formations, etc., depicted in the views of drawings are referred to by the same reference numerals. Well 6 is preferrably cased with common casing 14. It is used to pass oxygen-containing gas, which is normally air or oxygen-enriched air, down to the coal seam 10 to provide the combustion-supporting gas for partially burning the coal in seam 10 to destructively distill same in situ. Holes 12 are desirably provided through the well casing 14 to pass the air into the combustion zone 16 in coal seam 10 during operation. lnlet 118 communicates with the well 6 to supply the oxygen-containing gas (air) for carrying on the new method of the invention. An output or chimney well 20 is established by drilling same through coal seam 10 at a preselected and suitable distance from input well 6, preferably it has been found from 50 to 500 feet from well 6. The chimney well 20 is also preferably cased with inlet holes 22 through casing 24 providing for passage of the combustion gases produced in the coal seam 10 into output or chimney well 20. Upon drilling wells 6 and 20 into communication with coal seam 10, if coal seam 10 or any immediately adjacent formations are not satisfactorily permeable for gas passage therethrough, it has been found desirable to provide the passageways through the coal seam 10 by the fracturing, drilling or shooting methods of the art, as discussed hereinbefore, prior to equipping the wells for operation. It has been found desirable to fracture the formations from both wells. In this regard, the fracturability of the seam determines the maximum effective distance wells 6 and 20 can be located apart. Condensates in the combustion gas resulting from destructive distillation of coal in seam during operation condenses to a considerable extent in the coal seam downstream from the combustion zone and in chimney well 20. To collect the condensates 26 it is desirable to provide a sump section in the bottom of well 20, and to recover the same pump means 28 with rod 29 and tubing or conduit 30 are provided to raise the condensates to the surface and pass same via line 31. In operation the gaseous fluids resulting from the mining of the coal are passed from seam 10 through holes 22, up well 20, out outlet 32, and to condensing and recovery means 34, where the condensibles are removed from the gases and recovered via line 36 by suitable methods such as condensing and/or absorption known to the prior art. The process is made to operate, and is made controllable to provide for optimum mining and recovery by utilizing pumping or compressing means 38, the exhaust of which in operation is a gas suitable for use as fuel gas or for enrichment to make a suitable fuel gas. With the passageway established down through the well 6, through coal seam l0, and up well 20, to the ground, the coal seam 10 is ignited adjacent the hole l2and well casing 14 by any suitable means, for example, by electrical means, or an air-supplied gas burner lowered into the bottom of the well, why lowering into the well an ignited thermit mixture, and to ensure ignitionpure oxygen can be discharged into the well. Operation of the new method is then caused to be carried on through the operation of compressor 38 to draw oxygen-containing gas through inlet 18 into well 6, down therethrough and into coal seam 10. The key to the operation is providing flow through the passageway established from inlet 18 in pipe 6 to outlet 32 in pipe 20, by providing with exhaust means 38 a pressure in outlet 32 less than atmospheric, and a pressure in coal seam 10 less than the normal formation pressure. This allows for close and optimum control over the temperature and degree of destructive distillation of the coal in seam 10 in operation; Combustion-supporting gas causes the combustion front 16 to move through the coal seam to the well 20. The temperature of combustion to result in optimum destructive distillation of coal can easily be controlled by the amount of oxygen in the combustion supporting gas, or by the volume of combustionsupporting gas, easily controlled by valve means (not shown) regulating inlet 18, or by varying the speed of exhaust means 38. It has been found that a combustion temperature in the range of 900 to 1, 100 F. is desirable for optimum destructive distillation of bituminous coal such as found in stratified association with oil sands in Pennsylvanian and other geological formations. Through the passageway previously established in coal seam 10, gases resulting from the partial burning of the coal pass to pipe and enter such through holes 22. Condensate resulting in pipe 20 and that which passes from the coal seam into the pipe 20 collects in the sump in the bottom of pipe 20, and is pumped to the surface through tubing 30 for recovery. The gaseous fluids pass up through pipe 20 and out outlet 32 into recovery means 34 wherein the higher boiling constituents are recovered in any suitable manner such as by condensation, absorption, etc. The light ends are exhausted by compressor or exhaust means 38.

FIG. 2 depicts another preferred specific embodiment of the new method of the invention wherein the coal in seam 10 is mined by destructive distillation in situ, and petroleum in the overlying oil sand 40 is mined at the same time,. the petroleum mining being aided and assisted by heat energy passed from coal seam 10 as a result of combustion therein to oil sand 40 by conduction through the intervening layer 50 of kerogen, and by heat of convection passed to oil sand 40 by the combustion gases resulting from burning of the coal in seam 10. In this embodiment, furnace well 42 having casing 44 is established from ground level 8 down into communication with coal seam l0, and the casing is provided with holes 46 to pass combustion-supporting gases into coal seam 10 during operation. Tubing 48 is provided to convey the oxygemcontaining gas down into the bottom of the well 42, and such passes through plug 52 which seals around tubing 48 and plugs casing 44 to provide a collecting sump for petroleum from oil sand 40 and condensate from gaseous fluids produced in operation and passed to well 42 through holes 54 in casing 44 adjacent oil sand 40. In this embodiment, well 42 serves as the output well for gaseous fluids produced, and as the housing for the input of combustion-supporting gases through conduit 48. Chimney well 56 is established from the ground 8 down into communication with coal seam 10, and this well is cased by casing 58. Well spacing normally is less than in the embodiment of FIG. 1, but still usually in the range of 50 to 500 feet apart. Holes 60 are made through the wall of casing 58 to provide for passage of combustion gases from coal seam 10 into well 56 and holes62 are made in casing 58 adjacent oil sand 40 to pass the combustion gases from the well 56 to the oil sand 40, through the passageway established therein, and out holes 54 to output well 42. Plug 64 seals well 56 at the top of oil sand 40 so that the combustion gases have to pass into and through oil sand 40. The combustion gas temperature and pressure at this point are preferably sensed by thermocouple 66 and pressure-sensing tap 68, to aid in controlling the process for optimum recovery and mining. In operation, gaseous fluids produced pass from well 42 into separating means 34 through outlet 32. Condensates produced in separating means 34, as before are withdrawn through line 36, and compressor or exhaust means 38 which causes the method to function exhausts gases suitable for fuel. Petroleum and condensate produced and collected in the sump above plug 52 in cas ing 44 are pumped through tubing 70 to the surface and out of outlet 72. Oil sand 40 and coal seam 10, after drilling the wells 42 and 56 are perforated and the passageways established therein between the wells in any suitable manner as discussed hereinbefore, that is, preferably by fracturing, drilling, or shooting, and desirably in this embodiment formations permeability is established from each of the wells. In operation the coal is ignited adjacent holes 46 and the rich combustion gases resulting from the destructive distillation at the front '16 in coal seam 10 pass through the coal out holes 60, through casing 58, through holes 62, through oil sand 40 where they are further enriched and where they heat by convection the petroleum in oil sand 40 to lower the viscosity and/or volatilize a portion of same, and the resulting gaseous fluids pass out of oil sand 40 through holes 54 into well 42, up the well and out through outlet 32 into separating means 34 wherein the higher boiling constituents are recovered by suitable condensing and/or absorbing methods, with the recovered liquid materials being produced through line 36 and the light ends produced as fuel gas from the exhaust of pumps 38. By varying the oxygen in the oxygen-containing gas supplied through tubing 48 or by controlling the volume of such gas, the temperature of combustion at front 16 in the coal seam is regulated for optimum destructive distillation and recovery in mining the coal. The heat energy produced by coal combustion is then utilized to optimumly mine the petroleum in oil sand 40, Once operation is established, temperature and pressure sensed by thermocouple 66 and pressure top 68 can be followed in relation to production and recovery to provide for the same being at a maximum. It has been determined that in this specific preferred embodiment this occurs at a coal combustion temperature in the range of 900 to 1,100 P. for bituminous coals in the Pennsylvanian and other geological formations.

FIG. 3 schematically depicts another highly preferred specific embodiment of the new process of the invention, and such is quite similar to that depicted in FIG. 2 discussed in detail hereinbefore. The principal difference is that the new method of the invention is shown applied to a situation wherein it is desired to mine by destructive distillation the coal in a coal seam and the petroleum in an oil sand wherein the coal seam lies underground over and above the oil sand stratum, and wherein a stratum of rock or shale separates the coal seam and oil sand. This is a common situation in Pennsylvanian and Mississippian geological formations. Furnace well 75 is established from ground level 8 down through coal seam 10, rock or shale stratum 50 and oil sand 40 to a point below the latter. For operation well 75 is cased with casing 77 and a collecting sump for condensate and petroleum 79 is provided in the bottom of the well. The chimney well 81 is drilled from ground level 8 down through coal seam 10, rock or shale stratum 50, and through oil sand 40. This well is preferably cased with casing 83. Well spacing, it has been found, is advantageously the same as that with the embodiment of FIG. 2, and fracturing the formations is comparable. The coal seam 10 and the oil sand 40 are provided with passageways between the wells 75 and 81, if the stratum is not sufficiently porous, by a fracturing, drilling or shooting method known to the art, as discussed hereinbefore. This is conveniently done prior to equipping of the wells. Well casing 77 is perforated to provide holes 85 and 87 through which communication occurs between coal seam l and oil sand stratum 40 and well 75, respectively. Well casing 83 is provided with holes 89 and 90 to provide fluid communication between coal seam and oil sand 40, and well 81, respectively. A plug 91 seals well 75 at the top of oil sand 40. Well 81 is sealed by plug 64 at the top of coal seam 10. The usual pump 93 with tubing 95 and rod 97 is installed for pumping liquid fluids 79 to the surface for recovery via line 99. In this embodiment the combustion-supporting gas enters well 75 and casing 77 through inlet 101, and it passes down through well 75, though holes 85 to combustion zone 16 in the coal seam 10 during operation. Tubing or conduit 103 extends down through well 75 and plug 91 into the zone adjacent oil sand 40. Tubing 103 conveys to the surface and separator means 34 the gaseous fluids produced by the operation to mine the coal and petroleum. Thermocouple 66 and pressure-sensing tap 68 are desirably installed in well 81 to sense and indicate pressure and temperature so that the conditions of operation can be controlled to that which optimally mines the coal by destructive distillation, and the petroleum from the oil sand by partial volatilization and by recovery of the liquid portions in the usual collecting sump and pumping manner. With the wells and equipment established and installed, to commence the process, the coal in coal seam 10 is ignited in the vicinity of holes 85 in well casing 77 in a manner as described hereinbefore, relative the other specific preferred embodiments of the new method of the invention. Compressor or exhaust means 38 operates to reduce the pressure at ground level in conduit 103 to less than atmospheric and the pressures in coal seam 10 and oil sand 40 to less than normal formation pressure. As a result oxygencontaining gas (normally air) passes through inlet 101 into well 75, down the well, and through hole 85 in casing 77 and to the combustion zone 16 wherein the oxygen therein combines with the combustible materials of the coal to partially burn same to result in destructive distillation thereof. The resulting gaseous fluids of combustion then pass through the passageways in coal seam 10, through the holes 89 into casing 83 of well 81, down well 81, through holes 90 in casing 83, through the passageways in oil sand 40 wherein by convection heat from combustion of the coal is utilized to partially vaporize the petroleum in oil sand 40 and lower the viscosity of the petroleum so that it is more readily and more optimally produced. Enriched gaseous fluids from oil sand 40 pass thereout through holes 87 in casing 77 of well 75, up through tubing or conduit 103 and into separator and recovery means 34 wherein by condensation and/or absorption liquid fluid recovery is made, and the recovered liquids produced through line 36 while gaseous fluid recovery is exhausted as fuel gas by compressor or exhaust means 38. In operation, for process control, pressure can also advantageously be sensed by tap 105. Liquid fluid condensate 79 in well 75, and from the stratum being mined during operation, is pumped to the surface and recovered via line 99. As described hereinbefore in relation to the other preferred specific embodiments, the oxygen content of the combustion-supporting gas supplied via inlet line 101 can conveniently be adjusted control the temperature of combustion at front 16 in coal seam 10, or the volume of such gas can be varied either by regulating the effect of vacuum creating means 38, or by controlling valve means (not shown) in inlet 101 to control the combustion temperature and thus the degree of destructive distillation in situ of the coal and the volatilization of petroleum in oil sand 40. Heat energy resulting from combustion of the coal at front 16 is passed by conduction through the kerogen strata 50 to oil sand 40 to partially volatilize petroleum and/or lower the viscosity of same for better and more complete recovery. In Pennsylvanian and other geological formations, for .this preferred embodiment of the invention, it has been found that a combustion zone temperature of 900 to 1,100 F. is desirable for efficient operation.

FIG. 4 depicts another preferred specific embodiment of the new method of the invention for mining petroleum in an oil sand stratum 40, and coal in a coal seam stratum 10, such having therebetween a shale or rock geological formation 50, again the situation common to Pennsylvanian and other geological formations. The specific embodiment schematically and diagrammatically depicted in FIG. 4 is quite similar to that so shown in FIG. 2 hereof and discussed hereinbefore in detail. The principal difference is that a substantially centrally located input or furnace well 108 for the oxygen-containing gas employed is generally centrally located to a plurality of chimney wells 110 spaced therefrom. Input or furnace well 108 is established from ground level 8 down through oil sand 40, kerogen stratum 50, and through coal seam 10. It is preferably cased with casing 112, normally after oil sand 40 and coal seam 10 are provided with passageways therethrough between furnace well 40 and chimney wells 110 by a suitable fracturing, drilling, or shooting method of the art as discussed hereinbefore. Well spacing has been found to be in this embodiment desirably approximately the same as in the case of the embodiment of FIG. 2. Adjacent oil sand 40 and coal seam 10 holes 114 and 116 are made through casing 112 therearound, respectively. As in the other embodiments of the new method of the invention, these holes provide for passing gaseous fluid produced by the process into well 108, and passing oxygen-containing gas to the combustion front 16 in coal seam 10, respectively. Tubing or conduit 116 is placed in well 108 through packer or plug 118 to carry the oxygen-containing combustionsupporting gas to the bottom of well 108 for passage of such through holes 116 to the combustion front 16. Packer or plug 118 provides for a collecting sump thereabove in casing 112 for condensates from gaseous fluids in well 108 and petroleum produced from oil sand 40. In operation these liquid fluids are pumped to the surface through tubing or conduit 120 by the usual pump means operated by rod 122 in turn operated by a pump jack having a walking beam 124 and a powering source therefor 126. The liquids are produced through line 128. Chimney wells 110 are preferably cased with casing through which holes 132 and 134 are provided adjacent coal seam 10 and oil sand 40, respectively. In operation through holes 132 combustion gases pass from coal seam 10 into well 110, and through holes 134. These gases pass from well 110 into and through oil sand 40. The chimney wells 110 again are preferably provided with thermocouples 66 and pressure taps 68 to sense and indicate operating conditions so as to better control the process for optimum and maximum mining of the petroleum and coal. Separating means 34 and pump 38 are utilized in the manner discussed hereinbefore, relative the other embodiments of the process. In carrying on the method as depicted in FIG. 4, the coal in coal seam 10 adjacent holes 116 in casing 112 of well 108 is ignited, and through operation of pump 38 oxygen-containing gas is drawn down tubing 116 and through holes v1 16 to the combustion front 16 to support thereat destructive distillation of the coal. Resulting combustion gases pass through the passageways established in coal seam 10 out through holes 132 into well 110, up same, through holes 134 into and through the passageways established in oil sand 40 to partially ..through line 36. The light ends are produced as exhaust from pump 38. Liquid condensate formed in well 108 and liquids from oil sand 40 which collect in the sump above plug 118 during operation are pumped through tubing 120 to the ground and produced through line 128. The chimney wells 110 are plugged by plugs 136 at the top of oil sand 40 so that the combustion gases from coal seam are directed through holes 134 to and through the passageways established in oil sand 40. The degree of destructive distillation of coal in situ in I coal seam 10 is conveniently regulated by the oxygen content of the gas passed into tubing or conduit 116 by varying the volume of the gas by valve means (not shown) or by regulating pump 38 to vary the below atmospheric pressure at the surface in well 108. Here again, the new method of the invention is very easily and conveniently controllable to produce optimum mining of the coal and petroleum in the oil sand 40, as a result of such close control over the degree of destructive distillation of the coal in coal, seam 10, and by the utilization of heat energy produced, by the coal burning, by conduction through shale or rock 50 and byv convection through the combustion gases from coal seam 10 passed through oil sand 40 to partially volatilize and/or lower the viscosity of petroleum in the oil sand, and the great efficiency and recoveries made result from the pressure drop method through coal seam 10, oil sand 40, and at the surface where a pressure below atmospheric is utilized, with pressure during operation in coal seam 10 and oil sand 40 being below the normal formation pressures. In the preferred specific embodiment as depicted in FIG. 4, when applied to Pennsylvanian and other coal and oil sand strata, the combustion temperature in operation is preferably maintained in the range of 900 to l,lOO F.

The following are examples of the new method of the invention as applied to formations and situations as depicted in FIG. 2 of the drawings. However, it will be understood by those skilled in the art that such is applicable in teaching to the other preferred specific embodiments of the new method of the invention depicted in the drawings. Further, it is to be understood that the formations, operations, conditions, procedures, physical and chemical characteristics, and compositions, etc. set forth are illustrative of the new method of the invention only, and are not to unduly limit the scope of the invention.

EXAMPLES Examples, l-a through 3 tabulated below, report experiments simulating in the laboratory naturally permeable or artificially fractured formations through'which circulation of a fluid from a furnace well to a production well could be established. A 56-inch length of %-inch wall, 4 inch I.D. steel pipe was. supported so that its effluent end pitched downward approximately 5 from horizontal. In each experiment this pipe was filled and tamped with mineral matter that had first been screened through Ai-inch mesh. In each experiment the mineral core was ignited with a propane torch at the influent end of the pipe, and combustion was maintained as indicated, either with draft induced by suction or by draft forced with pressure. Somesignific ant conditions and results were:

EXAMPLE NO. 4

As illustrated by FIG. 3, two spaced wells are drilled through a coal seam 10, on through an intervening kerogen formation 50 and into an oil bearing sand 40 below it.

The oil sand is Bluejacket SS (Bartlesville) at a depth of approximately 225 to 260 feet from the top level to the bottom level, and the coal seam is Weir-Pittsburg approximately 38 inches to inches in thickness at a depth of approximately 215 feet. The analysis of the coal is moisture 5.79, volatile matter 32,34, fixed carbon 49.32, ash 12.55, sulfur 3.84, and

the calorific value is approximately 15,000 B.t.u. Both wells are cased down to the oil sand and are perforated at both levels. Both the oil sand and the coal are fractured from both wells, so that the areas of fracture overlap. Oil in the sand is of approximately 18 A.P.I. gravity and oilproduction from the sand cannot be achieved very economically naturally, even after the sand has been fractured.

One well 81, designated the duct well, is plugged above the coal seam level by plug 64. In the other well 75, designated the furnace-production well, two strings of tubing 95 and 105 are installed, so that one string 103 passes through a packer 91 located below the coal level and above the oil sand level. The second string of tubing 95 suspends a pump 93 below the packer in the sump, so that it may pump to the surface, liquids 79 that accumulate in the sump.

The vacuum pump 38 is connected, through a condenser 34 at the surface 8, to the casing of the furnace-production well 75. The pump 38 is started and the coal seam at the bottom of the furnace-production well is ignited. Air is pulled down through entry 101 and annulus of casing 77 to the combustion front 16 and combustion gases are pulled through the coal seam to the duct well 81, thence through the oil sand to the furnace-production well having casing 77 below packer 91 and up tubing 103 through the condenser 34 and through the pump 38 to its exhaust.

Following ignition, a chain of processes begins to take place approximately as follows:

The temperature in the coal seam 10 ahead of the combustion front 16 increases due to heat of convection from gases and liquids passing through it and due to heat of conduction through the coal itself.

Being so heated just ahead of the combustion front 16, coal devolatilizes. Still further ahead, condensablevolatiles reflux in the coal seam to partially dissolve it and increase the total ultimate yield of condensable hydrocarbons from the coal.

Heat is conducted through stratum 50 and the temperature of the oil sand 40 below the combustion front is increased, reducing the viscosity of the oil, which begins to ooze into the furnace-production well 75 below packer 91.

As the temperature of the coal seam near the duct well 81 Average Example rate Number Mineral Draft Air supply combusion Product and yield l-a Bituminous coal dry, 7% ash 36% Forced by pressure.. Atmospheric 1 it./hour. 4% coal as tar and 100 F.

vol. 4% sulphur. condensate. Balanee-150 B.t.u. gas.

1-b do .410 "d0 1in.lh0ur 7% of coal as tar and 100 F.

g condensate. i-c do d0.. relative humidity at 125 F do. 12% of coal as tar and F.

I condensate. l-c'l do ..do atmospheric intake pressure do... 33% coal as tar and 100 F.

(zpg/idensate. Gas1% H25. 2 Layer of gypsum (top half) over Induced by suction- 90% relative humidity at F. 2 in.lhour Gas 1.6% 11 Gypsum 50% layer oi coal. reduced to oxide.

3 Layer 0! coal (top half) over sand .....do Atmospheric 3 in./h0ur 50% ot pitch drained 011 as hot-coated with 20% petroleum pitch.

heavy oil.

NOTE: In the case of the experiments where How was induced by suction, control was much better.

increases, gases from it flowing back through the sand 40 a crease the temperature of the sand by heat of convection.

As operation continues gases flowing back through the sand 40 from the duct well 81 contain appreciable amounts of condensable coal volatiles, which are readily miscible with the oil in the sand, which markedly reduces its viscosity and which wash much of the oil out of the sand.

EXAMPLE NO. 4-a During operation as described in Example No. 4, between 1 pint and 1 gallon of water is metered into the air intake line with each 1,000 s.c.f. air, and this increases the yield of condensable coal volatiles.

EXAMPLE NO. 4-b During operation as described in Example No. 4, a portion of the exhaust from the vacuum pump 38, is stored under pressure in a vessel. Cyclic circulation is implemented for periods of from five (5 minutes to two (2) hours by-closing the air intake 101 when the intake line begins to show appreciable rise in pressure, and vacuum pump 38 is stopped and the stored gas in the vessel is permitted to flow back into the furnaceproduction well 75 below packer 91.

It is to be understood that this disclosure is not to unduly limit the scope of the invention, which we claim as follows:

1. A method of recovering hydrocarbons from a geological formation having therein a combustible organic material comprising,

a. establishing a passageway from a point in said geological formation, through same, and to the surface of the ground, igniting the combustible material in said formation,

c. passing an oxygen-containing gas into the resulting combustion zone by establishing in said formation a pressure lower than normal formation pressure upstream of said combustion zone and a pressure drop from said combustion zone to a point outside said formation through said passageway, and controlling the temperature of combustion at a temperature less than could be maintained with an adequate amount of oxygen in said oxygen-containing gas, and only partially volatilizing said organic material, and

d. passing resulting gases to the surface of the ground.

2 The method of claim 1 wherein said combustion is carried on at a temperature in the range 600 to 1,250" F.

3. The method of claim 1 wherein,

a. said geological formation is a stratum of bituminous coal,

b. said oxygen-containing gas is principally air, and said combustion is carried on at a temperature in the range of 900 to l,100 F., and

c. distillates are recovered from said resulting gases passed to the surface of the ground.

4. A method of recovering hydrocarbons from geological formations having therein petroleum and other combustible organic material in different strata comprising,

a. establishing a passageway from a point in said stratum having said other combustible organic material, through same, through said stratum having petroleum, and to the surface of the ground,

b. igniting said other organic material,

0. passing an oxygen-containing gas into the resulting combustion zone by establishing in said stratum having said other combustible organic material a pressure lower than normal formation pressure upstream of said combustion zone and a pressure drop from said combustion zone to a point in said stratum having petroleum through said passageway, and controlling the temperature of combustion at a temperature less than could maintained with an adequate amount of oxygen in said oxygen-containing gas, and only partially volatilizing said organic material,

d. passing resulting gases through said stratum having petroleum, and

e. passing resulting gases to the surface of the ground.

5. The method of claim 4 wherein the temperature in said combustion zone is in the range of 600 to l,250 F.

14 8. A method of recovering hydrocarbons from geological formations having therein petroleum and other combustible organic material in different strata-comprising,

a. establishing two wells into said strata in communication therewith, and providing a gaseous fluid passageway from a point in said other organic material stratum, through said stratum to one of said wells, through said stratum having petroleum, and to the surface of the ground,

. igniting said other combustible organic material,

c. passing an oxygen-containing gas into the resulting combustion zone by establishing in the stratum having said other combustible organic material a pressure lower than normal formation pressure upstream of said combustion zone and a pressure drop from said combustion zone to the surface of the ground through said passageway to a pressure less than atmospheric, and in said zone con trolling the temperature of combustion by controlling the oxygen available for combustion at a temperature less than could be maintained with an adequate amount of oxygen in said oxygen-containing gas, and producing for recovery volatilized organic material,

d. passing resulting combustion gases through said stratum of other organic material and volatilizing other organic material,

e. passing resulting gases through said stratum having petroleum therein and volatilizing a portion of same,

f. passing resulting gases through said passageway to the surface of the ground, and

g. while passing heat from said combustion zone into said stratum having petroleum therein by conduction.

7. The method of claim 6 wherein said combustion is carried on at a temperature in the range of 600 to 1 ,250 F.

8. The method of claim 6 wherein combustion is carried on at a temperature in the range of 900 to 1, F.

9. The method claim 6, wherein,

a. the stratum having petroleum is an oil sand, the one having the other combustible organic material is bituminous coal, and there is a stratum of kerogen separating them, neither of said two wells being in communication with said stratum of kerogen,

b. said oxygen-containing gas is principally air passed into said coal stratum by lowering the pressure in said passageway at the surface of the ground, and said combustion is carried on at a temperature in the range of 900 to 1,100" F.,

c. the viscosity of said petroleum in said oil sand is lowered by heat from said resulting gases passed through same,

(1. said petroleum in said oil sand stratum is lowered in viscosity by said heat passed thereinto by said conduction, and

e. petroleum and distillates are recovered in one of said wells and pumped to the surface of the ground therefrom.

10. A method of recovering hydrocarbons from geological formations having therein petroleum and other combustible organic material in different strata comprising,

a. establishing a well into said strata in communication therewith,

b. establishing a plurality of other wells spaced from said first-named well and each other and not in a line therewith and in communication with said strata,

c. with each of said other wells and said first-named well providing a gaseous fluid passageway from a point in said other organic material stratum to the one of said other wells, through said stratum having petroleum, and to the surface ofthe ground,

d. igniting said other combustible organic material between said first-named well and each of said other wells,

d. passing an oxygen containing gas into the resulting combustion zone between said first-named well and said other wells by establishing in the stratum having said other combustible organic material a pressure lower than normal stratum pressure upstream of said combustion zone h. passing resulting gases through said passageways to the surface of the ground, and

i. while passing heat from said combustion zone to the stratum having petroleum by conduction.

11. The method of claim wherein combustion is carried on at a temperature in the range of 900 to l,100 F.

12. The method of claim 10, wherein,

a. .the stratum having petroleum is an oil sand, the one havingthe other combustible organic material is bituminous coal, and there is a stratum of kerogen separating them. none of said wells being in communication with said stratum of k erogen,

b. said oxygen-containing gas is principally air passed into said coal stratum by lowering the pressure in said passageway at the surface of the ground, and said combustion is carried on at a temperature in the range of 900 to l,l00 F.,

c. the viscosity of said petroleum in said oil sand is lowered by heat from the said resulting gases passed through same,

d. said petroleum in said oil sand stratum is lowered in viscosity by heat passed thereinto by said conduction, and

e. petroleum and distillates are recovered in said firstnamed well and pumped to the surface of the ground therefrom. 

2. The method of claim 1 wherein said combustion is carried on at a temperature in the range 600 to 1,250* F.
 3. The method of claim 1 wherein, a. said geological formation is a stratum of bituminous coal, b. said oxygen-containing gas is principally air, and said combustion is carried on at a temperature in the range of 900 to 1,100* F., and c. distillates are recovered from said resulting gases passed to the surface of the ground.
 4. A method of recovering hydrocarbons from geological formations having therein petroleum and other combustible organic material in different strata comprising, a. establishing a passageway from a point in said stratum having said other combustible organic material, through same, through said stratum having petroleum, and to the surface of the ground, b. igniting said other organic material, c. passing an oxygen-containing gas into the resulting combustion zone by establishing in said stratum having said other combustible organic material a pressure lower than normal formation pressure upstream of said combustion zone and a pressure drop from said combustion zone to a point in said stratum having petroleum through said passageway, and controlling the temperature of combustion at a temperature less than could maintained with an adequate amount of oxygen in said oxygen-containing gas, and only partially volatilizing said organic material, d. passing resulting gases through said stratum having petroleum, and e. passing resulting gases to the surface of the ground.
 5. The method of claim 4 wherein the temperature in said combustion zone is in the range of 600 to 1,250* F.
 6. A method of recovering hydrocarbons from geological formations having therein petroleum and other combustible organic material in different strata comprising, a. establishing two wells into said strata in communication therewith, and providing a gaseous fluid Passageway from a point in said other organic material stratum, through said stratum to one of said wells, through said stratum having petroleum, and to the surface of the ground, b. igniting said other combustible organic material, c. passing an oxygen-containing gas into the resulting combustion zone by establishing in the stratum having said other combustible organic material a pressure lower than normal formation pressure upstream of said combustion zone and a pressure drop from said combustion zone to the surface of the ground through said passageway to a pressure less than atmospheric, and in said zone controlling the temperature of combustion by controlling the oxygen available for combustion at a temperature less than could be maintained with an adequate amount of oxygen in said oxygen-containing gas, and producing for recovery volatilized organic material, d. passing resulting combustion gases through said stratum of other organic material and volatilizing other organic material, e. passing resulting gases through said stratum having petroleum therein and volatilizing a portion of same, f. passing resulting gases through said passageway to the surface of the ground, and g. while passing heat from said combustion zone into said stratum having petroleum therein by conduction.
 7. The method of claim 6 wherein said combustion is carried on at a temperature in the range of 600 to 1,250* F.
 8. The method of claim 6 wherein combustion is carried on at a temperature in the range of 900 to 1,100* F.
 9. The method claim 6, wherein, a. the stratum having petroleum is an oil sand, the one having the other combustible organic material is bituminous coal, and there is a stratum of kerogen separating them, neither of said two wells being in communication with said stratum of kerogen, b. said oxygen-containing gas is principally air passed into said coal stratum by lowering the pressure in said passageway at the surface of the ground, and said combustion is carried on at a temperature in the range of 900* to 1,100* F., c. the viscosity of said petroleum in said oil sand is lowered by heat from said resulting gases passed through same, d. said petroleum in said oil sand stratum is lowered in viscosity by said heat passed thereinto by said conduction, and e. petroleum and distillates are recovered in one of said wells and pumped to the surface of the ground therefrom.
 10. A method of recovering hydrocarbons from geological formations having therein petroleum and other combustible organic material in different strata comprising, a. establishing a well into said strata in communication therewith, b. establishing a plurality of other wells spaced from said first-named well and each other and not in a line therewith and in communication with said strata, c. with each of said other wells and said first-named well providing a gaseous fluid passageway from a point in said other organic material stratum to the one of said other wells, through said stratum having petroleum, and to the surface of the ground, d. igniting said other combustible organic material between said first-named well and each of said other wells, d. passing an oxygen containing gas into the resulting combustion zone between said first-named well and said other wells by establishing in the stratum having said other combustible organic material a pressure lower than normal stratum pressure upstream of said combustion zone and a pressure drop from said combustion zone to the surface of the ground through said passageways to a pressure less than atmospheric, and in said zone controlling temperature of combustion by controlling the oxygen available for combustion at a temperature less than could be maintained with an adequate amount of oxygen in said oxygen-containing gas, and producing for recovery volatilized organic material, f. passing resulting combustible gases thrOugh said stratum of other organic material and volatilizing other organic material, g. passing resulting gases through said stratum having petroleum therein and volatilizing a portion of same, h. passing resulting gases through said passageways to the surface of the ground, and i. while passing heat from said combustion zone to the stratum having petroleum by conduction.
 11. The method of claim 10 wherein combustion is carried on at a temperature in the range of 900* to 1,100* F.
 12. The method of claim 10, wherein, a. the stratum having petroleum is an oil sand, the one having the other combustible organic material is bituminous coal, and there is a stratum of kerogen separating them, none of said wells being in communication with said stratum of kerogen, b. said oxygen-containing gas is principally air passed into said coal stratum by lowering the pressure in said passageway at the surface of the ground, and said combustion is carried on at a temperature in the range of 900* to 1,100* F., c. the viscosity of said petroleum in said oil sand is lowered by heat from the said resulting gases passed through same, d. said petroleum in said oil sand stratum is lowered in viscosity by heat passed thereinto by said conduction, and e. petroleum and distillates are recovered in said first-named well and pumped to the surface of the ground therefrom. 